It is known to culture Neisseria gonorrhoeae and other CO.sub.2 requiring organisms in a culture medium retained on an elongated member which is removably positioned in a closed container such as is shown in U.S. Pat. No. 3,616,265. It is known to the art to employ a carbon dioxide (CO.sub.2) tablet usually containing sodium bicarbonate and an organic acid, such as citric acid, in the bottom of the container to provide carbon dioxide which is desired to facilitate the culturing of the organism. In the presence of moisture the tablet releases CO.sub.2. Considerable difficulty has been experienced due to the fact that the amount of moisture available to the tablet varies greatly. Frequently, excessive moisture condenses in the container forming a pool of water surrounding the tablet causing a rapid evolution of carbon dioxide within minutes producing a higher than usual pressure and a greater leakage through the closure and reducing the length of time that carbon dioxide is present in the container to an unsatisfactory time period. This difficulty is remedied by the invention by providing means to secure a CO.sub.2 tablet to the elongated member supporting the culture medium at a point between the culture medium and the open end of the container to positively prevent the tablet from being exposed to an accumulation of water. This results in a relatively even release of carbon dioxide due to the interaction of moisture in the air within the container and the tablet assuring the presence of carbon dioxide within the container for a period of time sufficient to carry out the desired culturing, for example, 2 days.